Currently, the majority of autonomous and mobile electronic systems are powered by electrochemical batteries. Although battery quality has substantially improved over the last two decades, their energy density has not greatly increased. At the present time, however, factors such as cost, weight, limited service time and waste disposable problems (all intrinsic to electrochemical batteries) are impeding the advance of many areas of electronics. The problem is especially acute in the portable electronics space, where rapidly growing performance and sophistication of mobile electronic devices lead to ever-increasing power demands that electrochemical batteries are unable to meet.
One of the technologies that holds great promise to substantially alleviate the current reliance on electrochemical batteries is high-power energy harvesting. The concept of energy harvesting works towards developing self-powered devices that do not require replaceable power supplies. In cases where high mobility and high-power output is required, harvesters that convert mechanical energy into electrical energy are particularly promising as they can tap into a variety of high-power-density energy sources, including human locomotion.
High-power harvesting of mechanical energy is a long-recognized concept which has not been commercialized in the past due to the lack of a viable energy harvesting technology. Traditional methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric, or electrostatic do not allow effective direct coupling to the majority of high-power environmental mechanical energy sources. Bulky and expensive mechanical or hydraulic transducers are often required to convert a broad range of aperiodic forces and displacements typically encountered in nature into a form that is accessible for conversion using those methods.
Recently a new approach to energy harvesting using microfluidic devices that substantially alleviates the above-mentioned problems has been proposed. In particular, a high-power microfluidics-based energy harvester is disclosed in U.S. Pat. No. 7,898,096, entitled METHOD AND APPARATUS FOR ENERGY HARVESTING USING MICROFLUIDICS, inventor: Thomas Nikita Krupenkin, granted Mar. 1, 2011, and in U.S. Pat. No. 8,053,914, entitled METHOD AND APPARATUS FOR ENERGY HARVESTING USING MICROFLUIDICS, inventor: Thomas Nikita Krupenkin, granted Nov. 8, 2011, both of which are incorporated by reference herein in their entirety. The disclosed Krupenkin energy harvester generates electrical energy through the interaction of thousands of microscopic liquid droplets with a network of thin-film electrodes and is capable of providing several watts of power. In one preferred embodiment of this technique, a train of energy-producing droplets is located in a thin channel and is hydraulically actuated by applying a pressure differential between the ends of the channel. Such an energy generation method provides an important advantage as it allows efficient direct coupling with a wide range of high-power environmental mechanical energy sources including human locomotion.
A new method for energy harvesting using microfluidic devices that improves on the teaching of the above-cited Krupenkin patents has also been under development by the inventors and provides a new energy generation method and an apparatus that combine, in a synergistic way, the microfluidic-based electrical energy generation method described in these patents with the classical magnetic method of electrical power generation based on Faraday's law of electromagnetic induction. The resulting approach has a number of substantial advantages over the teaching of these Krupenkin patents, since it allows for effective energy generation without the need for an external bias voltage source. This improves the reliability and simplifies the harvester design in comparison with the teaching of U.S. Pat. Nos. 7,898,096 and 8,053,914.
However, the energy generation methods disclosed in these various references are not free from some shortcomings. In particular, no provision is made in any of these disclosures for allowing a continuous revolving motion of a chain of energy-producing elements within an energy-producing channel. The revolving motion of an energy-producing chain has a number of important advantages over the other types of motion of the chain, such as reciprocating motion. In particular, the revolving motion of an energy-producing chain allows the use of energy-producing chains and channels with substantially shorter lengths, thus enabling a more compact design of the harvester device. Another advantage of utilizing revolving chain motion is the ability to sustain a smooth, continuous motion by inertia for some time after the hydraulic actuation of the chain stops. This sustained motion extends the power generation time, and thus leads to a better energy harvesting efficiency.
Therefore, a method and an apparatus that can provide continuous revolving motion of a chain of energy-producing elements within an energy-producing channel would be highly beneficial, as it would improve the energy harvester device design and increase its efficiency.